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Radiant barrier in attic - both under rafters and over insulation?

Hello, I am thinking about installing Radiant Barrier type product in my attic to save on energy costsI was reading over the recommended installation methods and most of them say to install it under the rafters in the attic OR over the insulation on the attic floorDoes it make sense to install Radiant Barrier on BOTH the rafters and over the insulation? Or does that create a worse oven that what already exists in an attic without Radiant Barrier?

Answer:

How about no radiant barrier at all? The whole concept is rather dubious and at times borders on being a scamPretend for a minute that you can see infrared (heat) and that it was much like regular lightA radiant barrier is supposed to reflect infrared - so if you put it on the rafters it would reflect heat radiating from the ceiling back to the ceiling, and heat from the roof, back to the roofAs a regular conductive insulator, it is almost worthless You would be much better off using regular fiberglass insulation because most of the heat transfer is via conduction and not radiationSpend your money on sealing air leaks through pot lights and openings in the ceiling, and then add as much regular insulation as you can affordThe best place for a reflective coating in the summer would actually be outside the roof - e.ga reflective roof to keep it coolMany studies have been performed on radiant barriers and they all point to dismal resultsNot so much because they don't work - but because radiation is not the primary method of heat loss/gainI will add a few links below for you to ponderIf you like doing this kind of things, by all means set up some experiments - but be aware that your savings may be negligibleYou mention in the first sentence to save on energy costs so I assume your primary motivation is monetaryIt would be worthwhile to get someone to come in with a thermal imaging camera (sometimes called a thermal audit) and give you some color photos pinpointing where you are losing the most energyThen you can concentrate your efforts and money on where it is really neededThe last link below has some infrared photos I have taken of ceilings with defects that you should find interestingGood luck with your project.
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